U.S. Pat. No. 3,901,574 discloses an electrical connector including a plug and receptacle threadably fastened to one another by a flexible plastic coupling ring. Lug means on the flexible coupling ring pass over boss means contained within the matable threaded sections causing the coupling ring to deform so that the lug means seat in position adjacent the boss means emitting an audible sound in so doing.
U.S. Pat. No. 4,059,324 discloses an electrical connector having a plastic coupling member freely rotatably mounted on one housing member matably engagable with another housing member. The coupling member and the other housing member are threadably connected together to connect the matable housing members and the electrical contacts therein. A projection and slot arrangement is located on the coupling member and the other housing member which, when mated at the fully-mated condition of the housing members, visually indicates such condition.